All the extracted image data were merged to create a month long exposure map for the month.

The exposure map is opened with ds9, and check a distribution of count rates against energy.
From this, estimate the upper threshold value. Any events beyond this upper threshold are
assumed erroneous events such as bad pixels.

Using this upper threshold, the data is filtered, and create a cleaned exposure map for the month.

The exposure map from each month from the Sep 1999 is added up to create a cumulative exposure
map for each month.

Using fimgstatistic, we compute count rate statistics for each CCDs.

For observations with high data drop rates (e.g., Crab nebula, Cas A), we corrected the

observations by adding events.

Note: Counts and RMS's of Cumulative maps are lower than the previous months.
This is because we excluded extreme outliers.

Gratings

We plot the width of the zero order streak of ACIS/HETG observations and
the width of the zero order image for HRC/LETG observations of point sources.
No significant defocusing trend is seen at this time. See
Gratings Focus
pages. (NOTE: the figures are not updated from Mar 2009 due to a system problem.)

PCAD

Fid light positions on ACA drift with time. The drift trends of Fid light 2 with
ACIS-I and ACIS-S configurations are shown below.

The top panel shows Fid light 2 drift in ACENT I (app. along with -Y axis), and the
bottom panel shows that in ACENT J (app. along with Z axis). The unit is a pixel, and
one pixel is approximately 0.5 arcsec. The slope listed at the top right corner is
the change in a position per year (arcsec/yr). The vertical line on DOM = 1411 (Jun 1, 2003)
indicates a transition date of use of IRU-1 to IRU-2.
See also Tom Aldcroft's updated page:
https://cxc.cfa.harvard.edu/mta/ASPECT/fid_drift